This invention relates to a fireplace grate having a generally air-impervious fuel support plate with, when desired, several ash-screening slots in the center and joined along the front edge with an upstanding front rim having a plurality of passageways to supply front air for combustion over the top of the fuel on the support plate through the operation of draft control members.
Some of the other fuel support grates are made up of generally parallel bars on which the fuel is supported. The fuel on the grate ignites in the presence of a bottom draft whereby the combustion process takes place under the fuel, thus causing less efficient burning, overheating of the grate, poor radiation, and pollution because the heat is directed up through the center of the fireplace to the chimney directly above the fire. The cold down draft is pulled down along the outside walls to the bottom of the fireplace before it turns in to join the center updraft.
In chimneys leading from a fire, burning in a grate, there is a continuous cycle of moving air. The hot expanded gases generated above the burning fuel move up in a column through the center of the chimney. A stream of cold, dense, heavier air is pulled down around the outside of this column to the hearth of the fireplace. This cold air cools the walls of the fireplace as it flows down to the hearth. The cold air turns in, toward the center along the hearth of the fireplace, then up through the grate to the burning fuel where it is heated and pushed up the chimney with the hot gases. Other grates are inefficient because their design contributes to this type of inefficient fireplace burning. In some grates, a 3-4 inch space exists between the outside edges of the grate and the fireplace walls. This space permits the cold down draft to go down around the outside of the grate to the hearth of the fireplace before turning up through the grate. Since the down draft drops down from all sides, the updraft is then concentrated under the center of the grate bottom where it causes the fire to burn with intense heat like a forge and the bottom of the grate will burn out.
Special grates have been proposed in the past for the support of fuel during combustion in a fireplace. One such grate is shown in U.S. Pat. No. 4,173,967 and generally comprises a flat refractory tray with rear and side edge parts movable into a sealed relation with the walls of a fireplace. Downwardly-extending flanges support the tray above the hearth and provide space for the flow of air from the bottom to an elongated enclosure in the center which rises from the top surface of the grate. The opening at the bottom of the enclosure communicates with the space below the grate. A draft control mechanism under the grate includes a valve plate with control levers to regulate the flow of air from the bottom of the tray through the draft control enclosure into the space above the tray. The front flange is solid and detachable or hinged to the tray to form an upstanding barrier so that incoming air from the room is compressed and accelerated by the venturi effect created by the angled front barrier. The flange also serves to prevent incoming air from entering the low-pressure region within the tray directly. The raised draft control structure in the center of the grate causes center burning from the bottom while the outside walls are cooled by the cold down draft on the outside walls, which will increase the flow of heat up the chimney because air is supplied through center openings in the bottom part of this structure. Moreover, accumulation of ashes and cinders on the fuel support surface of the grate will clog the air-supply openings. Ashes cannot be efficiently or adequately separated from the unburned fuel. This mixture can only be disposed of by manual removal from the top surface of the grate. The use of refractory brick to form a lining on the top surface of the plate inhibits desirable radiation of heat, from the grate, which is then lost up the chimney. The grate disclosed in this patent is designed in the same manner as a forge. The concentrated center bottom draft will cause intense heat to be generated in the center of the grate. Heat generated in this area is surrounded by cold air and is pushed up the chimney. Because of the intense heat in the center where burning occurs, rapid deterioration will occur, i.e., a burning out and warping of the draft control mechanism. Ashes and cinders can drop down to clog the draft opening and the movable control plate under the bottom. The extension of the draft control housing up into the body of the grate would interfere with the arrangement and stoking of fuel in the grate. Center bottom burning will waste heat and cause excessive smoking. The cold down draft would be allowed to cool down the fireplace walls and push the heat toward the center of the grate.
To obviate the foregoing disadvantages of known forms structure for accommodating the combustion of fuel in a fireplace, the present invention provides an improved construction and relationship of parts to not only reduce the escape of heat through the chimney but also insure a safe, more efficient controlled burning of fuel. The fuel is burned at each end of the grate over a solid bottom by draft supplied from the front through openings at each end of the front rim and controlled by sliding doors. The slotted center section of the grate, when open, is kept free of fuel. An upward flow of air through this section spreads the flames over the top of the fuel toward the walls of the fireplace. The fire burns up along the sides, back and inside of the front rim, all of which radiate heat to the room.
The present invention is designed to radiate heat into the room like a stove, produce less smoke while burning in a controlled, fuel-saving manner. The design offers particularly significant advantage for a 24-hour burning period with only one filling of coal but somewhat less when wood logs are used. The grate of the present invention is designed for burning of fuel just inside of a front rim, along both sides and along the back of the fireplace. The walls of the fireplace as well as the front rim are heated and more efficiently radiate heat to the room. The cold down draft cannot fall below the burning site because the cooler air turns in over the fuel burning site from where it is heated and pushed up the chimney. The flow of air over the top of the fuel supports efficient top burning. There is no burning from the bottom so the grate does not overheat and firebrick is not necessary. The bottom is solid except for several slots, e.g., approximately 1/2 inch wide in the center, which extend from front to rear, to allow finely-burned ashes to drop to the hearth of the fireplace. This occurs when the remaining partially-burned fuel is moved over the slotted area before restoking. The new fuel is added to the end-burning area. The partially-burned fuel is then shoveled back over the top of the new fuel to burn from the top down. The center slotted area is kept open to supply needed draft up over the fuel. Some air flows over the top of the front rim from the room which also helps to support combustion over the top of the fuel. Draft control doors slide on tracks on the outside of the front rim and are located at each end. There is a special draft door in the center. These doors supply the necessary draft needed to control the fire. Air entering at the ends of the grate supports burning at each end next to the walls. The fire is started just back of and above the end doors. When burning logs lengthwise, a small removable plate may be placed over the slotted area to prevent inefficient center burning. If the logs are cut shorter and do not extend over the slotted area, the removable cover plate is not necessary.